Gravity Creates Weightlessness?

It is a very common misconception that when astronauts are in orbit they are weightless because they are somehow far enough from the earth that the force of earth's gravity does not pull on them. This is totally INCORRECT! If they were that far away, earth's gravity would not pull on the shuttle either and it would be impossible for it to be in orbit around the earth.

In this animation we see that the force of gravity (a force we call weight) is actually responsible for keeping the space craft and the astronaut in orbit around the earth. Gravity is still pulling on the astronaut. The feeling or impression of weightlessness comes from the lack of a force from the ground (normal force) having to push on your feet to keep you up. When that force is gone, we feel say we feel "weightless." In fact, whenever a person is in freefall they feel weightless even though gravity is still causing them to have weight. While in orbit, the space shuttle does not have to push on the astronaut (or anything else in the cabin) to keep him up. The space shuttle and the astronaut are in a constant state of freefall around the earth.

The idea of a constant state of freefall may be hard to imagine at first.
• Begin by picturing what would happen if the shuttle had no horizontal velocity...it would simply accelerate to the ground.
• If it had a little horizontal velocity, (give it some by pressing the up arrow) it would move forward as it fell but would still hit the ground.
• With a little more horizontal velocity it would move farther before running into the earth.
• With just the right amount of horizontal velocity it would fall toward the earth but at the same time it would miss hitting the earth. This constant state of freefall is what gives the astronauts an illusion of weightlessness.
• Increasing the horizontal velocity even more would result in an elliptical orbit similar to that of a comet.

Notice that in all cases, the vertical acceleration is approximately 9.8m/s2 toward the center of the Earth. Only in the case of the eccentric elliptical orbit does the distance between the earth and the shuttle become large enough to dramatically reduce the acceleration due to gravity.